1. The variations in production of type IV collagenase were studied after adding the tumor promoter, TPA, to normal and metastatic cells. This study shows an increase in the secretion of type IV collagenase by human melanoma (A2058), fibrosarcoma (HT1080) and mouse skin fibroblast (NIH-3T3) cell lines. On the other hand, no increase in the production of type IV collagenase could be found after treatment with TPA of two different primary human fibroblast cell lines. The optimal concentration of TPA was also studied and the maximum stimulation was obtained with 10-8 to 5 x 10-7 M TPA. 2. A new type IV collagenolytic assay was developed using activated p-nitrophenyl glass beads. The glass beads were coupled with radiolabeled type IV collagen, stored at 4 degrees C and then used for the assay. The binding of type IV collagen to the beads was studied with respect to tissue and temperature.